Britain's postwar status would turn on war length and the atomic project

What would Britain's postwar status be if the United States stayed out of the war?

It depends on how victory is achieved: prolonged conventional war could exhaust Britain, while ending the war as the sole atomic power would produce a very different position.

Britain's postwar position depends on whether Germany is defeated through prolonged conventional warfare or by an independent British atomic weapon. Both the British and American nuclear programmes are described as making progress before their combination accelerated development. Under wartime pressure, the independent British programme is judged capable of producing a weapon around 1946 or 1947. Britain as the only atomic power would occupy a different position from a country that had exhausted itself economically to grind Germany down.